<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>这是demo6</title>
    <script src="./jquery-3.7.1.min.js"></script>
    <style>
        #div1 {
            color: red;
            font-size: 30px;
        }
    </style>
</head>

<body>
    <div id="div1"><span>我是一个div</span> </div>
    <button id="button1">点击一下修改样式</button>
    <script>
        $("#button1").click(function () {
            let a = $("#div1").css("font-size", "20px");
            console.log(a);
        })


    </script>
</body>

</html>